I have tested it on and off here at the SSWT forum and it tends to have a low CTR (click through rate) - which brings the overall CTR in my account down. I was told that played in to the quality of ads that displayed on my sites across the board and lowered my revenue potential. It didnt bring in enough clicks/revenue to warrant the chance, and I decided the space was better used with specific promotions instead.

The only way to know is to test it, and of course you'll want to test various formats/placements, and just keep a close eye on it.

I am a member of many many forums and none have any adsense on them. I would say it is better suited for sites that have a good amount of traffic and where people are there for the purpose of looking to purchase something.

I have dabbled with adsense in the past and really gotten nowhere fast with it myself, I decided to put my energy into areas that I know will bring in income and yet be more targeted.

I have adsense on my forum. I've tried putting the code between the posts, but I find it gets ignored. I now have just a single Leaderboard banner at the top of every page (in the header) and it does ok. CTR is very low with forums though.